Many fluids that are transported or stored must be held in containers and protected from leakage. Some fluids pollute the atmosphere or the ground water, others are poisonous and some are simply too expensive to be lost. Some fluids may be maintained at atmospheric pressure while others must be stored under pressure. For many reasons it is important to detect when a vessel storing such fluids leaks and to prevent a leak that occurs as soon as possible.
In the past preventing leakage of fluids from storage vessels was accomplished by building the vessels with greater structural integrity and by using sophisticated inspection techniques to find sites that may ultimately become leak sites. Another technique for preventing leakage is to build double-walled vessels so that leakage from an inner vessel is contained by the outer vessel.
The term vessel includes above-ground and under-ground storage tanks, under water storage tanks, tanks mounted on trucks or trains and ships as well as piping through which fluid is transported. The term leakage connotes the act of leakage, i.e. the escape of fluid through a hole or opening in a vessel wall. The term leak site connotes the hole, crack, perforation or opening through which leakage occurs.
In spite of the leak prevention measures that have been taken, leakage has inevitably occurred. As a result a technology grew to detect leakage before too much damage was done to the environment or too much valuable material was lost. Leakage detection techniques range from simple monitoring of liquid levels in a storage vessel to detecting the presence of escaping material in the atmosphere or the ground by electronic or chemical means. The objective of all of these leak-detection systems is to learn of the presence of leakage before too much material escapes and to take protective measures to stop the leakage before too much fluid escapes. In other words, these systems must have an escape of fluid through a leak site before the systems become activated to indicate that leakage exists.